The role of Immune Complexes in the pathogenesis of Systemic Lupus Erythematosus will be further defined. Primary emphasis will be placed on the isolation and characterization of undetermined types of complexes and certain low molecular weight anti complementary substances that are detected in serum by precipitation with the Clq component of complement. In addition to studies on their role in the disease process, clues to possible etiologic agents will be sought in their composition. Microtubular cytoplasmic structures which are present in skin cell cultures which have been established from SLE patients will be studied in various ways. Special efforts will be made to determine any possible relationship of these structures to viral agents. Other SLE studies will focus on the association of congenital C2 deficiency and manifestations of SLE which have recently been observed. The possibility that complement deficiency states predispose to SLE will be explored. Studies on other related conditions will include investigations on the role of anti globulins in the nephritis of a variety of immune complex disease and further definition of a possible new clinical syndrome characterized by Erythema Multiforme and Hypocomplementemia.